Thermionic insulated arc welding gun

ABSTRACT

Improved means of insulating that portion of an air cooled arc welding gun which extends between the handle portion and the head portion to prevent thermionic emission dense enough to establish the conductance of welding current between it and the weldment, improved means for enclosing the welding current circuit suspended within the handle of the gun within a tube composed of insulating material to reduce the amount of heat radiated from the circuit within the handle, and improved means for suspending a highly heated welding current circuit within the handle to provide space between the wall of the handle bore and the suspended heated circuit for the circulation of cooling air therethrough. Also disclosed is the method of making the improved structure.

United States Patent Bernard et al.

1451 Apr. 17, 1973 THERMIONIC INSULATED ARC 3,197,611 7/1965 Morris etal ..2l9/130 WELDING GUN 2,914,598 11/1959 Spillane ..174 15 2,386,46610/1945 Hyde ..l74/121 [75] Inventors: Arthur A. Bernard, Beecher;

Richard A. Bernard, Flossmoor, FOREIGN PATENTS OR APPLICATIONS both Of1,094,703 12/1967 Great Britain ..219/I36 [73] Assignee: Bernard WeldingEquipment Company, Beecher, 111. Primary Examiner-J. V. Truhe iAssistant Examiner-George A. Montanye [22] Flled' 1970 AttorneyJames P.Hume et al. [21] Appl. No.: 100,518

[57] ABSTRACT Related US. Application Data Improved means of insulatingthat portion of an air Division Of 818,954. April 24, 1969 aban' cooledarc welding gun which extends between the donedhandle portion and thehead portion to prevent thermionic emission dense enough to establishthe con- [52] US. Cl. ..2l9/l30, 219/74, 219/136 ductance of weldingcurrent between it and the weld; [51] lllt. Cl. ..B23k 9/00 ment,improved means for endosing the welding cup [58] Fleld of Search ..2l9/I41, I36, 130, rem circuit Suspended within the handle of h gun 219/75,74; 285/133, 138; 287/58; 174/28, within a tube composed of insulatingmaterial to 88 C reduce the amount of heat radiated from the circuitwithin the handle, and improved means for suspending References Cited ahighly heated welding current circuit within the handle to provide spacebetween the wall of the handle UNITED STATES PATENTS bore and thesuspended heated circuit for the circula- 2,842,656 7/1958 Nevvirth..2l9/75 tion of cooling air therethrough. Also disclosed is the3,510,623 5/1970 Wolgast ..2 19/] 38 X method of making the improvedstructure, 3,265,856 8/1966 Cecil ..2l9/l30 I 2,444,767 7/1948 Cobean..219/75 4 Claims, 3 Drawing Figures 32 I6 N l 2 '6 gqgy E 1 i 7 Li,fimsi'asass'aasiss i w y A, 4 I F T -17 \\26 b k is INVENTORS ARTHUR ABERNARD RICHARD A. BERNARD. BY M W Mwrzz X/ fa ATTYS.

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m NN 5, AM 8 N 7 T// T /7/ //4///V-/ PATENTEBAPR 1 7 I975 A 7 /vf ///7 HQC 2 THERMIONIC INSULATED ARC WELDING GUN This is a division of US.application Ser. No. 818,954, filed Apr. 24. 1969, now abandoned.

This invention relates to an air cooled arc welding gun used forapplying continuous lengths of consumable electrode mechanically fedthrough the gun to the welding arc and, more particularly, to animproved means for heat insulating as well as electrically insulatingthat portion of an air cooled arc welding gun which extends in a curvedform between the handle portion of the gun to the head portion commonlycalled the gooseneck portion. This invention also includes the method ofmaking this improved structure.

Although primarily developed for guns which use a shielding gas from aseparate source, this invention is equally valuable when embodied in theconstruction of arc welding guns used for applying processes where theelectrode conveys materials to the welding are which are convertedintothe shielding medium when subjected to the heat of the welding arc and,also, for guns used for applying processes commonly called submerged arcwelding processes.

In the Bernard et al. US. Pat. application, Ser. No. 650,051, filed June29, 1967, now US. Pat. No. 3,469,070 an improved method of heatinsulating as well as electrically insulating the head portion of aircooled are welding guns is described and illustrated. However, in thatapplication the method used for shielding the gooseneck portion isconventional and therefore does not provide efficient heat insulatingmeans for shielding the gooseneck portion when the gun is used forhandling substantially higher than conventional welding currents.

The main object of this present invention, therefore, is to provide animproved method of insulating the gooseneck portion of arc welding gunsso as to handle a higher than conventional range of welding current sothat gun type arc welding can be moved up into a higher range ofefficiency. In this regard, it is important to understand that theincreased volume of welding heat produced by the increased volume ofwelding current heats the head portion of the gun to a destructivetemperature unless the heat absorbed by the head portion is constantlydrained from the head portion through the gooseneck portion into thewelding current cable connected thereto from which the heat radiates outinto surrounding space,

Obviously, when conducting these higher temperatures of heat from thehead portion, the gooseneck portion is heated to proportionately highertemperatures so high that the desired higher range of welding efficiencycannot be provided unless the problems caused by these higher heats aresolved.

For example, an are operating at 800 amperes heats the gas nozzle andthe welding current contact tip of the head portion to a red hottemperature and, indeed, would greatly exceed even a red hot temperatureand melt these parts of the head portion if it were not for the factthat the heat is constantly drained from the head portion through thegooseneck portion into the connected welding current cable. Obviously,the heat drained a temperature which breaks down and destroysconventional insulating materials.

Moreover, it is not enough to merely electrically insulate the outersurface of the gooseneck portion to prevent short circuiting should thegooseneck portion accidentally or intentionally contact the weldmentduring the welding operation since the volume of heat which radiatesfrom the gooseneck portion can produce a density of ions to ignite anarc between it and the weldment should the gooseneck even come close tothe weldment.

Further, a means improved beyond that disclosed in the above referred topending application had to be developed to shield the handle of the gunfrom the highly heated gooseneck portion within the handle so that thegun could be handled by the welding operator.

Heretofore, generally, there were two methods used for electricallyinsulating the gooseneck portion of arc welding guns. in the first ofthese two methods, the curved gooseneck portion is encased within a tubecomposed of rubber, silicon rubber, or neoprene, as referred to in theabove mentioned pending application. However, these insulating materialseither cannot withstand the ultra high temperatures the gooseneckportion is heated to and are thus rendered to a hard brittle state whichis fragile and cracks easily, or they have a very short life due to thescuffing to which this portion of the gun is subjected by the weldingoperator dragging the side of the gun along the surface of the workpieceto steady the arc and hammering this portion of the gun against theweldment to dislodge weld spatter which collects within the mouth of thegas nozzle and on the surface of the welding current contact tip withinthe nozzle.

In the second method which is used in several makes of guns, thegooseneck portion is electrically insulated by enclosing the curvedgooseneck portion within a curved metal tube with a space of aboutone-sixteenth inch to one-quarter inch between the outer surface of thegooseneck portion and the inner surface of the enclosing tube, and thisspace is maintained by the use of short length insulating bushingswithin the space at the ends of the outer tube. For certain makes ofguns of this second type, the space between the gooseneck portion andthe enclosing tube is used as a channelway for conducting arc shieldinggas to the head portion from ple of this second method is disclosed inUS. Pat. No.

' 3,112,392, dated Nov. 26, 1963. The disadvantages of this secondmethod are more critical than the disadvantages outlined above regardingthe first method because the gooseneck portion can reach a temperatureso high that the thermionic emission of ions from the gooseneck portionwithin the outer tube builds up to a density which ignites an arebetween the outer surface of the enclosed gooseneck and the innersurface of the outer tube when the outer tube contacts the weldment, andwhen this happens a small area of the outer tube melts and is rupturedas it is blown outward as the air of shielding gas is expanded by beingheated by the are within the space. Therefore, the following areotherimportant objects of this present invention:

1. To provide a gooseneck portion for an arc welding gun which isinsulated by a method that prevents an emission of ions from the heatedgooseneck portion dense enough to ignite an are between the weldingcurrent circuit and the base metal should the gooseneck portion closelyapproach but not actually contact the weldment when the welding circuitis alive.

2. To provide a means for electrically insulating the gooseneck portionof arc welding guns which prevents a direct short circuiting of weldingcurrent between the gooseneck portion and the weldment should thegooseneck portion actually contact the weldment when the welding circuitis alive.

3. To suspend the electrical conducting and heat conducting gooseneckportion within the center of space within the handle -to provide acirculation of air through the handle while shielding both thesuspending means and the inside surface of the handle from the heatedgooseneck portion with a layer of material which has high electrical andhigh heat insulating properties such as tightly woven glass filamentcords or asbestos fiber cord, sandwiched between the outer surface ofthe main tube or trunk of the gooseneck portion and a thin wall outertube which is not a portion of the welding current circuit and which isshielded from thermionic emission from the welding current circuit.

4. To provide a method for making the gooseneck portion of an arcwelding gun by telescoping a straight piece of copper tube or copperpipe into a tight fitting pliable tube made of tightly braided ortightly woven glass filament cords or asbestos fiber cords, telescopingthe glass filament tube or asbestos fiber tube into a straight piece ofthin wall metal tubing, and then with suitable discs to be clearlydescribed further on, bend the assembly of straight laminated tubes intothe radius and degree required to produce the shape of gooseneckdesired.

5. To provide a means for electrically insulating the gooseneck portionof arc welding guns which is rugged and can withstand hammering withoutbeing destroyed; and

6. To provide a means for insulating the gooseneck portion of arcwelding gun which will not be destroyed by the high temperature to whichthe gooseneck portion is heated when using unusually high weldingcurrents.

These and other objects, features, and advantages of this invention willbe better understood by reference to the following description and thedrawings in which:

FIG. 1 is a diagrammatic cross-sectional view of an air cooled arcwelding gun which embodies the inventive means for electricallyinsulating and heat insulating the gooseneck portion of the arc weldinggun.

FIG. 2 is a cross-sectional view taken across lines 2- 2 of FIG. 1.

FIG. 3 illustrates apparatus which may be used for forming the gooseneckportion of this invention.

Referring to the drawings, the arc welding gun illustrated in FIGS. 1and 2 is the type commonly called an air cooled type and is composedgenerally of a handle portion 10, a gooseneck portion 1 l and a headportion 12. The head portion or assembly 12 comprises a welding currentcontact tip 13 and a gas nozzle 14 carried on a head member 15. Thegooseneck portion 11 is attached to, yet suspended from, the handleportion by two spaced collars 16, each provided with threadedprojections 37 for attachment to the handle with screws 40. Attached tothe rearward end of the gooseneck portion 11 is a multi-purpose conduitand welding current cable assembly 17 which conducts the weldingcurrent, the consumable electrode 18, and the arc shielding gas to thegooseneck portion 11. These three materials are conducted through thegooseneck portion 11 to the head portion 12. The welding current isconducted from the welding cable 17 to the main tube member 19 of thegooseneck portion 1 l to the head member 15, to the contact tip 13, andfrom the contact tip 13 into the welding electrode 18 at the tip ofwhich the current is converted into the welding are 20. The areshielding gas (if used) flows through the bore 24 of the copper tube 19in the space between the electrode 18 and the wall of the bore 24.

Referring now specifically to the gooseneck portion 11 shown in FIGS. 1and 2, the main tube member 19 has a curved midsection and a straightsection at each end, and is made of extra heavy wall copper tube orpipe. The actual size of the tube or pipe is governed by the ratedwelding current capacity of the welding gun. If the gun is rated for 600amperes maximum at an percent duty cycle, the main tube member 19 ismade from V4 inch size extra heavy wall copper pipe, more specifically,a copper pipe 0.540 inch CD. by 0.294 inch ID. by 0.123 inch wallthickness. The copper pipe 19 is threaded at the end 22 within thehandle portion 10 with a tapered 1 inch national pipe thread forattachment to a fitting 21 to which the spiralled strands of the weldingcurrent conductor 26 and the flexible electrode conduit 27 are affixed.The forward end of the copper pipe 19 is also threaded at 28 forattachment to the head member 15.

Before the :41 inch copper pipe 19 is bent to the required angularextent and radius to produce the desired accurate shape of the gooseneckportion 11, a tightly woven yet pliable glass filament cord tube 29 istelescoped over the 54 inch size copper pipe 19. Preferably, the wall ofthe woven glass filament cord tube is not less than one thirty-secondinch thick. As previously mentioned, this electrical and heat insulatingtube 29 may also be made of asbestos fiber or any other material whichhas equal heat and electrical insulating properties. To make thegooseneck portion of this invention, it is very important to understandthat if the woven glass filaments or asbestos fibers are not woven orcompressed tightly enough together, it is necessary to fill the smallopenings between the woven cords with silicon rubber or some other suchcompressible and stretchable material which can withstand a temperatureof 500 plus degrees Fahrenheit. This silicon rubber in pourable liquidform is applied by dipping or brushing and then permitted to solidify atroom temperature into a consistency of ordinary rubber. Then aspreviously mentioned, the glass filament tube 29 is telescoped into atight fitting brass or stainless steel tube 30 with a wall about 0.025inch thick. It is further important to understand that in the upperportion of the 500 to 800 amperage range of current, the heat which isconducted through the gooseneck portion into the connected welding cablecan be that high a temperature that even though the fine mesh betweenthe woven glass filament cords is sealed with silicon rubber, a smallamount of thermionic emission can penetrate through the insulation, andit is important that the build-up of ions be permitted to escape so thatit does not become dense enough to ignite short circuiting between theinner tube 19 and the outer tube 30. To prevent a dense build-up ofions, the thin wall outer tube 30 is provided with perforations 31. Thesize of perforations 31 need not be larger than 3/32 inch or Vs inchdiameter spaced at about three-eighths inch or one-half inch lengthwiseand circumferentially about the tube 30.

It should be noted in FIG. 1 that the insulating tube 29 extends beyondthe opposite ends of the outer tube 30 at 32 and 33. Extensions 32 and33 are provided to produce dimensions between the ends of the outer tube30 and the surface of the heated main tube 19 which exceeds the lengthof the welding are at the tip of the electrode 18 so that, should theouter tube contact the workpiece when the welding circuit is alive,arcing will not take place at these areas. In other words, in that thedimension of the are 20 is shorter, the welding current will continue toflow at the shorter arc dimension because it has the least resistance.

Referring now particularly to FIG. 2, it will be noted that the twocollars 16 which suspend the gooseneck portion 11 within the center ofspace within the handle portion 10 are both electrically insulated andheat insulated from the electrically and heat conductive main tube 19 bythe glass filament cord tube 29. I

In copending application Ser. No. 650,051, now US. Pat. No. 3,469,070the present two inventors claim the invention of providing a circularair duct through the handle of an arc welding gun to disperse heat fromaround the welding current circuit suspended therein and, therefore, donot claim this feature being a portion of this present invention.However, an important feature of the present invention is theimprovement that the heat conductive main tube 19 is also enclosedwithin the insulating tube 29 which greatly reduces the amount of heatreleased within the handle portion 10 and, further, the means used forattaching the suspended gooseneck portion 11 from the handle portion 10,namely, by collars 16, is a considerable improvement over that disclosedin the above mentioned copending application.

Still referring to FIG. 2, it will be noted that the outer tube which isinsulated from the main copper tube 19 telescopes through a bore 34 ofthe collars l6 and that collars 16 include internally threaded bosses 36for set screw which rigidly clamps collars 16 to the outer tube 30 ofthe gooseneck portion 11. Also included are the projections 37 which areinternally threaded for connecting the handle 10 to the gooseneckassembly with screws 40 as previously noted. For reasons which areobvious from the drawings, the attaching screws 40 are electricallyinsulated and heat insulated from the main tube 19 which conducts thewelding current and heat. With the exception of the locations where thefour small areas of the projections 37 contact the handle, the gooseneckportion 11 is totally suspended within the center of the space throughthe handle to provide a duct to convect heat out of the handle 10. Inactual practice, the collars 16 are made by extruding aluminum or brassin 10 or 12 foot lengths with the cross-sectional shape shown in FIG. 2,and then cutting the extruded shape into lengths of aboutnine-sixteenths inch. The collars may also be made of molded glassfilament cords or asbestos fiber cords bonded with a silicon material.

Referring now to FIG. 3, this drawing illustrates a very simple yet veryefficient method and apparatus for bending the assembly of straighttubes 19, 29, and 30 into the required curvature of the gooseneckportion. The operating principle is quite similar to that of bendingconventional conduit used for electric light and electric power wiring.The gooseneck portion is shown in elevation as 11' before bending and inphantom view as 11" after bending. To perform the bending operation, oneend of the gooseneck assembly 11' is placed under a first saddle shapedblock 46 and by applying pressure P to a second saddle shaped block 47,the assembly 11' is curved around a form fitting die surface 48 whichhas the radius and the degree of the curvature desired. Actually, theradius of the forming die 48 is slightly less than the actual radiusdesired to allow for spring-back. To retain the roundness of the tubes19, 29, and 30 as the assembly 11' is curved to the curvature of the die48, the die 48 is grooved to form-fit the outside diameter of the thinwall tube 30.

While a specific form of the invention has been described herein, it isto be understood that this is by way of example only and not by way oflimitation. It is contemplated that modifications will occur to thoseskilled in the art within the scope of the appended claims withoutdeparting from the spirit of the invention.

It should be noted that the insulating tube 29 may be referred toas asubstantially ion-impervious shield or insulator. By this, it is meantthat the tube 29 serves to prevent ion concentrations or arc-supportingdensity in the space occupied by the tube 29. In this sense it may besaid that the tube 29 serves to displace ionizing air or gas with aunitary, substantially non-ionizing material. The terms ion-imperviousand non-ionizing" do not preclude the de minimus presence or movement ofions in the material of which the tube 29 is formed.

What is claimed is:

1. In an arc welding gun for feeding continuous lengths of consumableelectrode in an arc welding process and which includes a handle memberhaving a bore through its total length, the combination therewithcomprising: a main tubular trunk for conducting welding current throughits wall and consumable electrode through its bore to a head assembly ofthe arc welding gun, said main tubular trunk having means at adownstream end connecting said main trunk to the head assembly of thearc welding gun, said main tubular trunk extending into the bore of saidhandle member and having means at an upstream end thereof connectingsaid main trunk to a welding cable, said main trunk comprising an innerelectrically conductive metal tubular member encased within asnug-fitting second tube of unitary electrical insulating andsubstantially ion-impervious material, said second tube being encasedwithin a third snug-fitting tube of thin gauge metal: and meanssuspending the portion of said main tubular trunk extending into thebore of said handle member to provide a space between the wall of thebore of said handle member and the outer periphery of said third tube ofsaid main trunk for the circulation of cooling air through the bore ofsaid handle member said suspending means comprising, one or more collarsthrough which said main trunk is telescoped, each of said collars beingrigidly attached to the outer periphery of said third tube of said maintrunk and having outwardly extending projections spacing said collarcentrally within the bore of said handle member and attaching saidcollar to said handle.

2. In an arc welding gun for feeding continuous lengths of consumableelectrode in an arc welding process and which includes a handle memberhaving a bore through its total length, a main tubular trunk forconducting welding current through its wall and the consumable electrodethrough its bore to a head assembly of the arc welding gun and having acurved midportion and a straight section at an upstream end thereof, anelectrically conductive fitting at the upstream end of the main trunkfor connection to a welding cable, and means coupling a downstream endof said main trunk to the head assembly of the arc welding gun, thecombination therewith of improved means for suspending said straightsection at the upstream end of said main trunk within the bore of saidhandle to enable the circulation of air through said handle bore andaround said main trunk comprising: one or more collars through whichsaid main trunk is telescoped and within collars having outwardlyextending projections for spacing said collar centrally within saidhandle bore and attaching said collar to said handle, and an improvedmain trunk comprising for at least the portion of its length betweensaid head assembly and said collars: an inner metal tubular memberencased within a snug-fitted second tube of unitary electricalinsulating and substantially ion-impervious material, said second tubebeing encased within a third snug-fitting tube of thin gauge metal.

3. The invention defined in claim 2 wherein said outwardly-extendingprojections are internally threaded for receiving screws attaching saidcollar to said handle and wherein said collar further includes aninternallythreaded boss for receiving a set screw rigidly-clamping saidcollar to said main trunk.

4. The invention defined in claim 2 wherein the said third tube of thingauge metal contains a plurality of perforations along its exposedperiphery.

- .UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatentNo.3,728,514 Dated p i117,. 973

Inventofls) Arthur A. Bernard and Richard A. Bernard It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

The name of the Assignee should read --Dover Corporation, New York, NewYork-- instead of Bernard WeldingEquipment Company,

Beecher, I1l' r In the Specification:

' Column 1, line 64, after "drained." insert -through the-gooseneckportion, in turn,,can heat this portion to-.

Column 3, line 28, change "discs" to read "dies".

C-olunm 3, line 37, change "gun" to read -g.uns--.

Column 6, line 29, change "or" to read f'--' Inthe Claims:

Column 8, line 6, change "snug-fitted" to read snug-fitting" Signed andsealed this 11th day of June 19714..

(SEAL) Attest:

EDWARD M.FLETCHER,JR. C. MARSHALL DANN Attesting Officer Comissioner ofPatents FORM PO-10 0 (1 uscoMM-oc 60876-P69 a U5. GOVIINIINY PRINTINGOFFICE I'll 0-366-384,

JUNITED STATES PATENT OFFICE CERTIFICATE OF' CORRECTION Patent No. 3 728514 Dated April 17,1373

Inventor(s) Arthur A. Bernard and Richard A. Bernard It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

The name of the Assignee should read --Dover Corporation, New York, NewYork-E instead of "Bernard Welding Equipment Company, Beecher, 111,". i

In the Specification:

v Column 1, line 64, after "drained'insert -through the gooseneckportion, in turn, can heat this portion tO 0 Column 3, line 28, change"discs" to read "dies".

Column 3, line 37, change "gun" toread --guns--.

Column 6, line 29, change "or" to read -.-'of-- Inthe Claims:

Column 8, line 6, change "snug-fitted" to read --snug-fitting Signed andsealed this 11th day of June 1971;.

(SEAL) Attest: I

EDWARD M.FLE'I'CHER,JR. C. MARSHALL DANN Attesting Officer Commissionerof Patents FORM powso (10459) d v USCOMM-DC 60376-P69 U. s. GOVIRNMENTPRINTING OFFICE I," 0-36-33l-

1. In an arc welding gun for feeding continuous lengths of consumableelectrode in an arc welding process and which includes a handle memberhaving a bore through its total length, the combination therewithcomprising: a main tubular trunk for conducting welding current throughits wall and consumable electrode through its bore to a head assembly ofthe arc welding gun, said main tubular trunk having means at adownstream end connecting said main trunk to the head assembly of thearc welding gun, said main tubular trunk extending into the bore of saidhandle member and having means at an upstream end thereof connectingsaid main trunk to a welding cable, said main trunk comprising an innerelectrically conductive metal tubular member encased within asnug-fitting second tube of unitary electrical insulating andsubstantially ion-impervious material, said second tube being encasedwithin a third snug-fitting tube of thin gauge metal: and meanssuspending the portion of said main tubular trunk extending into thebore of said handle member to provide a space between the wall of thebore of said handle member and the outer periphery of said third tube ofsaid main trunk for the circulation of cooling air through the bore ofsaid handle member said suspending means comprising, one or more collarsthrough which said main trunk is telescoped, each of said collars beingrigidly attached to the outer periphery of said third tube of said maintrunk and having outwardly extending projections spacing said collarcentrally within the bore of said handle member and attaching saidcollar to said handle.
 2. In an arc welding gun for feeding continuouslengths of consumable electrode in an arc welding process and whichincludes a handle member having a bore through its total length, a maintubular trunk for conducting welding current through its wall and theconsumable electrode through its bore to a head assembly of the arcwelding gun and having a curved midportion and a straight section at anupstream end thereof, an electrically conductive fitting at the upstreamend of the main trunk for connection to a welding cable, and meanscoupling a downstream end of said main trunk to the head assembly of thearc welding gun, the combination therewith of improved means forsuspending said straight section at the upstream end of said main trunkwithin the bore of said handle to enable the circulation of air throughsaid handle bore and around said main trunk comprising: one or morecollars through which said main trunk is telescoped and within whichsaid main trunk is rigidly clamped, each of said collars havingoutwardly extending projections for spacing said collar centrally withinsaid handle bore and attaching said collar to said handle, and animproved main trunk comprising for at least the portion of its lengthbetween said head assembly and said collars: an inner metal tubularmember encased within a snug-fitted second tube of unitary electricalinsulating and substantially ion-impervious material, said second tubebeing encased within a third snug-fitting tube of thin gauge metal. 3.The invention defined in claim 2 wherein said outwardly-extendingprojections are internally threaded for receiving screws attaching saidcollar to said handle and wherein said collar further includes aninternally-threaded boss for receiving a set screw rigidly clamping saidcollar to said main trunk.
 4. The invention defined in claim 2 whereinthe said third tube of thin gauge metal contains a plurality ofperforations along its exposed periphery.